# CVE-2021-22881: Actionpack Open Redirect Vulnerability

> Attackers can redirect users to malicious sites via crafted Host headers if allowed hosts use leading dots in Ruby on Rails Action Pack.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 11 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-22881, GHSA-8877-prq4-9xfw, UBUNTU-CVE-2021-22881

## What is CVE-2021-22881?

CVE-2021-22881 is a medium-severity vulnerability in Fedoraproject Fedora, published on 11 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

The Host Authorization middleware in Action Pack before 6.1.2.1, 6.0.3.5 suffers from an open redirect vulnerability. Specially crafted `Host` headers in combination with certain "allowed host" formats can cause the Host Authorization middleware in Action Pack to redirect users to a malicious website. Impacted applications will have allowed hosts with a leading dot. When an allowed host contains a leading dot, a specially crafted `Host` header can be used to redirect to a malicious website.

Weakness: CWE-601 (URL Redirection to Untrusted Site)

## Which versions are affected by CVE-2021-22881?

4 open source packages ship an affected version, including actionpack. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `actionpack` | RubyGems | From 6.0.0 | 6.0.3.5 |
| `actionpack` | RubyGems | From 6.0.0 | 6.0.3.5 |
| `actionpack` | RubyGems | From 6.1.0 | 6.1.2.1 |
| `actionpack` | RubyGems | From 6.1.0 | 6.1.2.1 |

Products: Fedoraproject Fedora, Rubyonrails Rails.

## How do I fix CVE-2021-22881?

Upgrade actionpack to a fixed version for your release line: 6.0.3.5 or 6.1.2.1.

## Is CVE-2021-22881 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-22881 exists.

Public exploit code:

- Ruby on Rails - Open Redirect via Host Header Injection (nuclei): http/cves/2021/CVE-2021-22881.yaml

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-22881 and fix it if it is affected.

What it is: CVE-2021-22881 is a medium-severity vulnerability in Fedoraproject Fedora, published on 11 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-22881 exists.

Affected packages and fixed versions:
- actionpack (RubyGems): affected from 6.0.0; fixed in 6.0.3.5
- actionpack (RubyGems): affected from 6.0.0; fixed in 6.0.3.5
- actionpack (RubyGems): affected from 6.1.0; fixed in 6.1.2.1
- actionpack (RubyGems): affected from 6.1.0; fixed in 6.1.2.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-22881/ (Markdown: https://insights.sbomify.com/CVE-2021-22881/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-22881
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-22881
- OSV: https://osv.dev/vulnerability/CVE-2021-22881

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-22881/
Summaries are generated and may contain mistakes; the official description above is the record.